Interacting Abiotic Factors Affect Growth and Aflatoxin B1 Production Profiles of Aspergillus flavus Strains on Pistachio-Based Matrices and Pistachio Nuts

Abstract

Pistachio nuts are an economically important commodity produced by many countries. They can be colonized by mycotoxigenic fungi, especially Aspergillus flavus, resulting in contamination with aflatoxins (AFs), especially aflatoxin B1 (AFB1), a Class 1a carcinogen. The objectives were to examine the effect of interactions between the two key abiotic factors, temperature and water activity (aw) on (a) in vitro growth and AFB1 production by four strains of A. flavus isolated from pistachio nuts, on a milled pistachio nut medium modified ionically (NaCl) and non-ionically (glycerol) in the range 20–35°C and 0.995–0.85 aw, (b) colonization of layers of raw pistachio nuts stored at different interacting temperature x aw conditions and on relative AFB1 production and (c) develop models to produce contour maps of the optimal and marginal boundary conditions for growth and AFB1 production by up to 4 strains of this species. On pistachio nut-based media, optimum growth of four strains of A. flavus was at 0.98–0.95 aw and 30–35°C. Optimum AFB1 production was at 30–35°C and 0.98 aw. No significant differences in growth was found on ionic and non-ionically modified media. Colonization of layers of raw pistachio nuts was slower and contamination with AFB1 significantly less than in in vitro studies. Contour maps based on the pooled data for up to four strains (in vitro, in situ) showed the optimum and marginal conditions for growth and AFB1 production. These data can be used to identify those conditions which represent a high, intermediate or low risk of colonization and AFB1 contamination in the pistachio nut processing chain. These results are discussed in the context of the development of appropriate intervention strategies to minimize AFB1 contamination of this economically important commodity.

Impacts of Climate Change Interacting Abiotic Factors on Growth, aflD and aflR Gene Expression and Aflatoxin B1 Production by Aspergillus flavus Strains In Vitro and on Pistachio Nuts

“…Indeed, optimal conditions for the growth of four strains of A. flavus from pistachios were found to be at 0.98-0.95 water activity (a w ) and 30-35 • C. AFB 1 production was also optimal at 30-35 • C and 0.98 a w . Interestingly, while less AFB 1 was directly produced on raw shelled pistachio nuts the optimum and marginal boundary conditions were similar [3].…”

“…The quality and safety of pistachio nuts for human consumption have been compromised by the infection of the ripening nuts, especially pre-harvest, when early splitting of the shells can allow colonization by members of the Aspergillus section Flavi group, predominantly A. flavus. In addition, poor drying and storage practices can also exacerbate infection by A. flavus post-harvest [2,3]. Such infection results in significant contamination with aflatoxin B 1 (AFB 1 ), a class 1a carcinogen [4].…”

“…This required the development of an effective Hazard Analysis Critical Control Plan (HACCP) with appropriate Critical, Control Points in this chain focused on more efficient harvesting and post-harvest management of pistachios from Iran to meet the necessary legislative limits. However, because they are rich in lipids, they can reabsorb moisture from the atmosphere during the post-harvest phase, allowing for further contamination [3].…”

“…A recent study of the water and temperature relationship of A. flavus strains isolated from pistachio nuts in Saudi Arabia showed that optimum growth on both pistachio nutbased media and raw pistachios was optimal at 35 • C in contrast to maize, where this is usually at 28-30 • C [3,9]. This certainly suggests that strains from pistachio nuts may have evolved to have better tolerance to high temperatures in production areas such as Iran and perhaps the USA from where the strains originated [3]. Indeed, optimal conditions for the growth of four strains of A. flavus from pistachios were found to be at 0.98-0.95 water activity (a w ) and 30-35 • C. AFB 1 production was also optimal at 30-35 • C and 0.98 a w .…”

Predictive Modeling and Validation on Growth, Production of Asexual Spores and Ochratoxin A of Aspergillus Ochraceus Group under Abiotic Climatic Variables

“…Recent studies have been conducted with Aspergillus section Circumdati ( A. westerdijkiae , A. ochraceus , A. steynii ) and section Nigri species ( A. carbonarius ) in vitro and on stored coffee beans in relation to OTA production under climate change conditions [ 15 , 16 ]. Currently, a significant interest has been expressed in the impact of abiotic climatic variables (temperature, water availability, and CO 2 ) and their interactions on the colonization of economically significant commodities with mycotoxic fungi and mycotoxins [ 17 , 18 , 19 , 20 ].…”